Add evaluation suite and prevent reassignment of labeled frames

[emdavis02]

Resolving Issue #11 and #6
Creating evaluation functions to easily test tracking methods in the future. Simultaneously added logic to never reassign a labeled frame's tracks, these frames are treated as ground truth.

[codecov]

Codecov Report

Attention: Patch coverage is 24.00000% with 76 lines in your changes missing coverage. Please review.

Project coverage is 66.66%. Comparing base (abf7f4e) to head (00d18f5).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
sleap_mot/eval.py	0.00%	63 Missing ⚠️
sleap_mot/tracker.py	74.07%	7 Missing ⚠️
sleap_mot/candidates/fixed_window.py	40.00%	3 Missing ⚠️
sleap_mot/candidates/local_queues.py	40.00%	3 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main      #12       +/-   ##
===========================================
- Coverage   77.33%   66.66%   -10.67%     
===========================================
  Files           7        8        +1     
  Lines         428      516       +88     
===========================================
+ Hits          331      344       +13     
- Misses         97      172       +75     

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